1. Field of the Invention
This application relates to an apparatus for continuous blending and, more specifically, to a continuous blender that is adaptable to produce different output rates.
2. Background Information
Continuous blenders are known in the prior art, see e.g., U.S. Pat. No. 3,341,182. Such blenders included an inlet chute, an initial mixing chamber and a zig-zag mixing tube with an outlet. The inlet chute had an opening into the mixing chamber. The mixing chamber had an outlet to the mixing tube. Generally, two or more, preferably dry, materials were introduced into the continuous blender via the inlet chute. The mixing chamber and the mixing tube were then rotated in order to mix the materials. The zig-zag tube was made from a series of V-shaped and inverted V-shaped sections. Thus, when the lateral axis of the zig-zag tube was in a vertical plane, the zig-zag tube had a series of peaks and valleys, with each vertex of a V-shaped or inverted V-shaped section being that peak or valley. As the zig-zag tube was rotated, the peaks and valleys were inverted.
In operation, the dry materials were introduced into the mixing chamber via the inlet chute. As the mixing chamber was rotated, the materials were partially mixed therein. When the zig-zag tube V-shaped section adjacent to the initial mixing chamber moved to a position wherein the vertex was below the mixing chamber outlet, a quantity of the partially mixed materials fell into the first V-shaped section. As the first V-shaped section was rotated and inverted, the materials fell onto the inverted vertex and a portion of the materials moved into the next V-shaped section, while another portion was returned to the initial mixing chamber. As the zig-zag tube continued to rotate, the process of a portion of mixed materials moving to the next section of the tube while another portion moved backward was repeated, thereby thoroughly mixing the materials. Eventually, a portion of the mix materials reached the zig-zag tube outlet and were discharged.
The initial mixing chamber and zig-zag tube are coupled together, or are formed from a unitary piece, and are called the shell assembly. The shell assembly was supported at least at both ends by trunnion rims having a generally circular outer edge and a disk having an opening therein. The trunnion rim opening was typically off-center. The zig-zag tube extended through the trunnion rim opening. The trunnion rims were disposed on casters attached to a mounting plate. An additional trunnion rim was coupled to a motor, typically by a chain drive. When the motor was operated, the chain drive caused the shell assembly to rotate about its longitudinal axis. The input tube was rigidly coupled to the mounting plate to ensure the inlet chute did not rotate with the shell assembly. A seal was located at the interface between the inlet chute and the shell assembly. It is further noted that the mounting plate included a tilting device whereby the shell assembly and input tube could be tilted.
In this configuration, the throughput of the continuous blender was controlled by three main factors; the size of the zig-zag tube (both diameter and length), the speed of the motor, and the degree of tilt of the mounting plate. The size of the zig-zag tube was fixed and could not be changed. Although the speed of the motor was adjustable, the range of motor speeds was still controlled by factors such as, but not limited to, the diameter of the shell assembly and centrifugal forces. The degree of tilt could be increased, that is the discharge end or the zig-zag tube could be lowered, or decreased, i.e. the discharge end could be raised. Of these factors, the size of the zig-zag tube had the greatest impact on the amount of material that could be blended and, as noted above, this was not adjustable. As such, the prior art continuous blenders were not very adaptable to different mixing requirements.
This type of continuous blending was improved by adding an “intensifier.” The intensifier was, essentially, a blender inserted into the initial mixing chamber. The intensifier included a shaft with a blade or paddle at the end. The shaft was disposed parallel to the longitudinal axis of the shell assembly and the paddles were located in the mixing chamber. The shaft included seals to reduce the amount of mixed materials from escaping. An additional chain from the motor acted to impart rotational movement to the intensifier shaft. As the intensifier shaft had a smaller diameter than the shell assembly, the intensifier shaft rotated at a greater speed. The disadvantage of adding the intensifier was that the intensifier shaft housing was typically disposed in the path of the inlet chute and could cause the materials to become “hung up.” This was especially a problem where there was a very little amount of one material and any delay in introducing that material to the mix could cause uneven mixing. Thus, even the improved continuous blender was not overly adaptable to different mixing routines.
Also, as noted above, various interfaces between the shell assembly and other components, e.g., the inlet chute and the intensifier shaft included seals to reduce the quantity of mix material that escaped. Not only were these seals subject to wear and failure caused by normal use, but were also subject to additional wear on the trunnion rims and the casters. That is, as the trunnion rims and casters would wear, the shell assembly would not rotate about the designed rotational centerline. In this condition, the wear on the trunnion rims and casters would create non-parallel sealing surfaces thereby creating gaps. The gaps at the sealing surfaces allowed the product to leak.
U.S. patent application Ser. No. 11/113,492 (hereinafter '492 application), from which the present application partially depends, provides a continuous blender having a drive unit with a shell assembly mounting and a shell assembly structured to be removably coupled to the shell assembly mounting by one or more clamps. The drive unit may be coupled to shell assemblies having different lengths and diameters. Thus, by changing the shell assembly coupled to the drive unit, the output of the continuous blender may be dramatically changed.
The continuous blender also includes an intensifier with a separate drive motor. The shell assembly motor and the intensifier motor are independent of each other. Moreover, both the shell assembly motor and the intensifier motor may be run intermittently, at various speed, and in reverse. In such configuration, the mixing capabilities of the continuous blender are highly adjustable. The speed of the shell assembly motor and the intensifier motor, as well as an adjustable tilting mechanism, are controlled by a programmable control unit. The control unit may be programmed with various parameters associated with selected formulations. As such, the continuous blender may be quickly switched from one formulation to another. In addition, for a given formulation the controls allow for real time adjustment to maintain the formulation within acceptable limits. The system also utilizes Process Analytical Technology to provide a feedback loop.
The '492 application also provides for a continuous blender wherein the zig-zag tube is cantilevered. That is, the zig-zag tube is not supported by trunnion rims. As such, there are fewer components subject to wear and tear. Additionally, the '492 application provides for an air purged seal with a spherical surface between the drive unit and the shell assembly. Such an air purged seal with a spherical surface is useful in maintaining a controlled seal interface in preventing product leakage on a drive unit assembly with a cantilevered shell assembly.
As use of a cantilevered shell assembly allows for rapid changing of a shell assembly, a kit as described herein may be provided having two or more shell assemblies having different throughput rates.